An animal model system has been established with C57BL/6J mice to study the influence of protein-calorie malnutrition on the primary immune response during the early postnatal development of the immune system. The present study will examine and characterize the impairments of the immune system of protein-calorie malnourished mice that result in delayed and decreased antibody production to sheep erythrocytes. Specially, the role of antigen processing by macrophages, suppressor cell populations, and physiologic environment in the processing by macrophages, suppressor cell populations, and physiologic environment in the impairment of the primary immune response of protein-calorie malnourished mice will be further characterized and defined. BIBLIOGRAPHIC REFERENCES: Impairment of the Primary Immune Response in Early-Onset Protein-Calorie Malnutrition. R. R. Hook, Jr. and D. P. Hutcheson. Nutrition Reports International, In Press, June, 1976.